Process and apparatus for the production of a heart valve prosthesis

ABSTRACT

An elastic textile covering is applied over an annular support of a heart valve prosthesis by inserting the preferably collar shaped textile covering through the annular support, turning two projecting axial ends of the textile covering over the outer surface of the annular support and then joining the two axial ends to each other to form a seam that preferably extends entirely around an outer periphery of the annular support. This seam can be concealed by a collar, which also may be covered by the textile covering. An apparatus for applying the textile covering to the annular support includes two coaxial annular rings into which the annular support and textile covering are inserted. Each of the rings includes structure for attachment to a respective axial end of the textile covering.

BACKGROUND OF THE INVENTION

The invention relates to a process for covering an annular support of aheart valve prosthesis with a textile covering, and to an apparatus forcarrying out the process.

The known prostheses used in cardiac surgery contain a crown-shapedannular element of plastic, but generally of metal or of both materials.They consist in general of long, often wire-like elements which arepredominantly not very elastic and are often joined by soldering orwelding. This results in poor adaptability, especially since the jointsthen become brittle, but in some cases also relatively poor tolerance,not least because the textile covering generally applied to the annularelement then requires several seams in order to hold securely on thewire skeleton of the annular element. This results in strength problemsand also can make manufacture more difficult. Typical heart valveprostheses of this type are described in U.S. Pat. No. 3,570,014 or U.S.Pat. No. 3,755,823.

SUMMARY OF THE INVENTION

It is the object of the invention to design a heart valve prosthesis ofthe type described above in such a way that the adaptability andtolerance are improved, strength problems being avoided. This isachieved according to the invention by covering an annular support of aheart valve prosthesis with a textile covering that is elastic at leastin one direction. The textile covering is pushed into the annularsupport and, at its two projecting axial ends, the textile covering isturned over the outer surface of the annular support. The two axial endsof the textile covering then are joined to one another by a seam, whichextends around the annular support.

By means of the process according to the invention, the textile coveringis mounted on the annular element with a minimum of seams. Thus, on theone hand, the tolerance improves since a plurality of thick seams isavoided but the strength is also improved as a result, since seamsalways entail a mechanical risk. It would of course also be possible toapply the process according to the invention to conventional annularelements, but it is precisely in combination with a particular,preferred support, disclosed herein, which provides results optimumresults.

Although the process according to the invention could also be realisedwithout an apparatus of a particular type, the apparatus according tothe invention not only considerably helps and facilitates theimplementation of the process and the production of a prosthesisaccording to the invention but also guarantees uniform quality throughthe clamping apparatus provided according to the invention. Thepreferred apparatus for performing this process includes two coaxialrings, which hold the annular support together with the textile coveringduring assembly. One of the rings includes a fastener for one end of thetextile covering. The other ring includes a clamping apparatus for theother end of the textile covering.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of the invention are evident from the followingdescription of embodiments shown schematically in the drawing.

FIG. 1 shows a heart valve prosthesis according to the invention beforeattachment of the biological heart valve material;

FIGS. 2 to 6 show the successive steps in carrying out the processaccording to the invention, starting from a rectangular piece ofmaterial according to FIG. 2; and

FIG. 7 shows an apparatus according to the invention for carrying outthis process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an oblique view of a heart valve prosthesis 1 according tothe invention with partly removed textile covering 3, which covers anannular support 1a together with a collar 2 attached thereto. As can beseen, the annular element 1a consists of flat material, in particular ofa thermoplastic, so that it can be produced easily and economically, forexample by injection moulding.

The support 1a possesses, in a manner known per se, three axiallyprojecting support arms 4, the free ends of which are rounded.Projections 5 and indentations 6 are arranged alternately on the axialend, the base B, of this support 1a, which end is opposite the supportarms 4, it being possible for any excess biological heart valve materialwhich is to be flattened in a conventional manner over the support armsand is to be fastened to the collar 2 to be accommodated in saidindentations.

The textile covering 3 is elastic and consists expediently of a networkfabric, because such a fabric has sufficient intrinsic elasticity--evenwhen conventional, biologically tolerated textile material is used. Inpractice, a USCI product, Adavison, from C. R. Bard, Catalogue No.007831, has proved expedient. This is all the more surprising sincenonelastic coverings have been chosen to date; however, it willsubsequently become clear that the choice of elastic material results ina simplification in the manufacture of the heart valve prosthesis,improved safety with respect to tearing of seams and a smaller number ofsuch seams, which also improves the tolerance of the prosthesis. This isbecause in many cases a concealed (and therefore invisible)circumferential seam in the region of the collar 2 will be sufficient,if necessary with a vertical seam 7.

In order to facilitate the process according to the invention--withoptimal anatomical fit--it is expedient if the support arms 4 arerounded at their free ends with the radius R which corresponds to notmore than one eighth of the diameter of the support 1a in the region ofits collar 2. On the other hand, it is advantageous if the indentations6 are relatively flat, the radius of curvature 2R preferablycorresponding to not more than twice the radius of curvature R of thesupport arms 4. The collar 2 shown in FIG. 1 and consisting of textileor plastic material is expediently mounted between two circumferentiallines, of which the upper circumferential line is preferably located adistance a1' of about 1 mm below the base 4a of the support arms 4 butthe lower circumferential line is advantageously slightly further awayfrom the edges of the indentations 6, so that a distance a2' of, forexample, 2 mm results.

In this context, it is therefore possible first to prefabricate annularelements 1a of different diameters, preferably from 17 mm to 33 mm atthe base B. In order thereafter to form a heart valve prosthesis shownin FIG. 1 therefrom, it is necessary to provide--in the mannerdescribed, a textile covering 3, which state had to be produced fromseveral individual parts, tediously and with several seams. It istherefore intended, with reference to FIGS. 2 to 6, to describe theprocess according to the invention, in which, starting from a piece ofmaterial closed in a collar-like manner, a single seam is sufficient.

According to FIG. 2, however, a prepared textile collar is not availableand must first be produced from a rectangular piece of material in themanner shown. This piece of material consists of a network fabric, forexample a knitted fabric, having a sequence of relatively dense strips12 formed from warp threads and sparser meshes 13 in between, which inparticular give the textile covering 3 elasticity in the direction ofthe arrow A' whereas it has slightly less elasticity in the direction atright angles thereto. A similar material has been put on the market byUSCI, Adavison, from C. R. Bard, U.S.A., under Catalogue No. 007831.

Whereas to date nonelastic coverings were used in spite of the largenumber of seams required, the elasticity of the textile covering 3 usedaccording to the invention allows the latter to be pulled over thesupport arms 4 and their base region 4a, differences in length beingelastically compensated. Of course, the covering 3 consists of medicallyor biologically tolerated textile material known per se.

Thus, in order to obtain the required collar form according to FIG. 3,the rectangular piece of material according to FIG. 2 is bent with itsends towards one another, and the ends are then connected to one anotherby a vertical seam 7 (cf. FIG. 1). As can be seen, it is preferable ifthe edges 14 of the material are provided with a bead in order toincrease the strength of the seam 7. To avoid outward-projectingmaterial residues in the covered support 1a, the collar with its bead onthe inside according to FIG. 3 is expediently turned outwards beforebeing pulled into the support 1a.

The collar-like fabric sleeve thus formed is pulled through the annularelement 1a from the inside according to FIG. 4, so that the collar 2 iscoaxial with said annular element and the axial ends of the textilecovering project above and below the annular element. From thisexplanation, it is of course clear that FIG. 3 merely shows a section ofthe collar, which--in order to be able to project above the support 1aand below the latter--must have a diameter which is substantiallysmaller than the length of the collar 3.

In any case, the upper projecting end 15 of the covering 3 can thus beturned outwards and downwards in the manner shown in FIG. 4, whereas thelower projecting end 16 is turned outwards from the bottom. If a collar2 (FIG. 1) is to be mounted, it is expedient if the lower end 16 ischosen to be slightly longer than the upper end 15, since it is intendedto be used for covering the collar 2. It is of course also clear thatFIG. 4 shows the covering 3 in a partially cut away view with thecentral strip omitted, since the collar 3 according to FIG. 3 does infact form a closed hollow cylinder. This section view according to FIG.4 is merely intended to illustrate the path of the two ends 15 and 16.

As soon as the two ends 15, 16 have been turned into the position shownin FIG. 4, all that is still required is a circumferential seam 17 tosew together the joining points 18 of the two ends 15, 16, which joiningpoints have been pulled together. Seam 17 is located a distance a1 fromthe base 4a of the support arms 4, and a distance a2 from the base B ofannular support 1a. If the starting material used was already acollar-shaped fabric, for example a hollow network article, the seam 17is the only seam required for the covering and, when a collar 2 ismounted, even this seam is covered by said collar. Instead of a hollownetwork article, it is also possible to use hollow knitted fabric,network material being preferred because it has intrinsic elasticitywhich is due to the method of production and is not associated with theuse of an elastic material, although such a material could also be usedwithin the scope of the invention, provided it is biologicallytolerated. As is evident and is confirmed in practice, this intrinsicelasticity above all compensates any difference in length which, in thecase of the support arms 4 with their base area 4a in between, isparticularly large. Nevertheless, there is no danger of overstretchingof the fabric 3, and the direction of extension along arrow A' of FIG. 2has proved in practice to be more advantageous than the reversedirection.

Once this point of the process has been reached, it is still necessaryto place a plastic piece or the like which forms a collar 2, and has across-section which is angular, for example rectangular, but accordingto FIG. 5 in this case triangular, on the projecting and the short end.15. It may be advantageous to fasten the collar 2 with the aid of a fewcross stitches 19 or zig-zag stitches 20 to the annular element 1a inorder to prevent slipping or twisting and for this purpose smallthrough-holes (not shown) may be made in the support 1a, in particularin the region of the upper circumferential line (cf. the upper limit ofthe collar 2), but in any case along the lower circumferential line(that is to say at the lower limit of the collar 2 or between theselines) in order to facilitate this connection.

The lower, longer end 16 is now folded over the upper surface of thecollar 2 (FIG. 6) and around the inner lateral surface of said collar insuch a way that the latter is covered by a section 21 and the former bya section 22. This is of course only necessary when the collar 2 is notitself formed from textile material or covering by the textile covering3 is desired for other reasons, said covering also being used foranchoring in the biological tissue. The turning over of the end section21 makes it possible to conceal this end and to fasten it to thecovering or, if necessary, also to the annular element 1a with the aidof a concealed seam 23, for which purpose the above-mentioned, verysmall through-holes arranged in the region of the circumferential linesdetermined by the collar 2 may be used.

By applying the concealed seam 23 in the region of the previouslyapplied seam 17 (FIG. 4), both seams are covered by the collar 2 in sucha way than, on the one hand, they are virtually completely invisiblefrom the outside or merge to form a single seam. However, this seam 23can of course also help to fasten the two end sections 15, 16 (FIG. 4),so that the seam 17 may be in the form of a relatively loose quiltingseam. In the final analysis, the appearance of the heart valveprosthesis 1 shown in FIG. 1 is then achieved.

To be able to carry out the process described above in a simplifiedmanner, it is preferable to provide an apparatus according to FIG. 7.This has essentially two rings 33, 34, the internal diameter of which issufficiently large to hold a complete prosthesis 1', that is to say aprosthesis 1' formed from support 1a and textile covering 3. A certainadditional play between the outer diameter of the annular element 1areinforced with the covering 3 and the internal diameter of the rings33, 34 makes it possible to apply an all-round seam at a point 24 withinthe internal diameter of the rings 33, 34, as will be explained below.

First, however, the annular element 1a, with collar 3 inserted throughfrom the inside, is placed in the inner opening 25 of the rings 33, 34.Thereafter, the lower end 16 is then expediently turned outwards overthe outer surface of the annular element 1a and is fastened carefully tothe lower ring 33 so that it rests with its end section 21', in eachcase with the same length over the entire circumference, on a supportsurface 26 of the ring 33. In this position, the lower end 16 isdetachably fixed, for example with the aid of a clamping ring 28. Thisclamping ring can be in the form of a spring ring or in the form of acircumferential ring which can be clamped, for example, with the aid ofa toggle lever apparatus (not shown), the first embodiment beingpreferred. In order to enlarge the clamping area, it is advantageous ifthe ring 33 has a circumferential seam 27 including the ring 26 togetherwith the piece of fabric clamped by it.

After the lower end 16 has been fastened to the lower ring 33 in thismanner, the upper end can be pulled over the support arms 4 and theregions 4a present in between. The upper end 15 is then fastened to theclamping apparatuses 29, which for this purpose are equipped withgripping elements 41, for example with hooks (as shown), but ifnecessary also with forceps-like grippers. These gripping elements 41are connected to tension elements, such as springs 30, and are subjectedto a lead by these, it being advantageous if the spring force isadjustable with the aid of an adjusting screw 40 in order to be able toadapt it to different prosthesis sizes. On the other hand, adaptationmay also be necessary when different coverings are used, since it willgenerally be necessary also to change the rings 33, 34 when the size ofthe prostheses 1' is changed, unless the diameter is adjusted byinserting a suitable sleeve into each of the rings 33, 34, which is alsopossible within the scope of the invention.

Furthermore, the section through the rings 33, 34 shows that the innersurfaces thereof are preferably inclined towards the clamping point atwhich the ends 15, 16 meet one another, in order to improve theaccessibility during sewing. To return to the clamping apparatuses 29,it may be mentioned that it is advantageous if the particular clampingforce set can be read on a scale 42 connected to the adjusting screw 40.In order to distribute the clamping force as uniformly as possible overthe circumference of the ring 34, a plurality of clamping apparatuses29, which is indicated merely by their axes 29', is expedientlydistributed over the circumference of this ring. In order to supportthese clamping apparatuses 29 on the outside of the ring 34, the latterconsists of an inner ring section 35 and an outer ring section 36 onwhich the clamping apparatuses 29 are fastened. This results in a cavity31 between the two ring sections 35, 36, in which cavity, as shown, thegripping elements 41 are housed.

Of course, FIG. 7 merely illustrates a preferred embodiment and it wouldbe quite possible to modify the ring 34 so that the gripping means 41are also readily accessible when rings 33, 34 are placed together, inwhich case it would also be possible to apply the seam 17 (cf. FIG. 4)not inside the opening 25 but instead just on the outside of the innerring section 35, in other words where the cavity 31 is located in FIG.7. However, this requires that, after the rings 33, 34 have beenslackened, the textile covering is placed around the annular element 1aunder less tension than when the seam is applied, in other words thefabric would have to be more greatly stretched during sewing, which onthe one hand would make measurement of the clamping force with the aidof the clamping apparatuses more difficult (where these can be providedat all) and on the other hand would give rise to the danger ofoverextension of the textile covering 3.

An apparatus as shown in FIG. 7 could also be used for applying adifferent type of seam connection if, for example, one of the two rings33, 34 or both rings 33, 34 are equipped with a heatable ring region,thus permitting heat bonding or welding of the two fabric ends 15, 16.However, a weld seam or bonded seam, the production of which isgenerally simpler, is generally thicker and especially less elastic thana sewn seam, which is therefore preferable for heart prostheses of thistype.

In order to hold the rings 33, 34 securely during the operationsdescribed above, it is expedient to provide a stand 51 which--forholding the support 1a at the desired working height--is advantageouslyprovided with a retaining bush 32 which is adjustable in height and canbe screwed to various depths into the stand 51.

The rings 33, 34, which are held in the indicated clamping position bycorresponding clamping means, such as clamping screws 44 or clamps,during application of the seam 17 (FIG. 4), are expediently guided onthe stand 51 with the aid of guide columns 37 but can be secured on thelatter in the position lowered towards the retaining bush 32 with theaid of adjusting rings 43 which can be moved along the columns 37 andclamped to said columns or with the aid of other blocking elements.After application of the seam 17 inside the opening 25, the collar 2 canbe mounted according to FIG. 5, after which the projecting end 15 is cutoff.

In practice, either a human (if desired also animal) pulmonary or aorticvalve is stored in a nutrient solution (together with antibiotics andother substances) and is sewn to the prosthesis described shortly beforeuse, or the already assembled components of the prosthesis are stored orfrozen together in a nutrient solution until they are required. Thisalso enables a high cell survival rate to be achieved, and theprostheses produced in this manner can be used in four differentpositions.

It should be mentioned that the positioning rings 43 constitute anadditional element for holding the rings in the lower position in theirmutual clamping position and thus, if necessary, facilitating subsequentpulling of the covering 3. Only when the fabric has been pulleduniformly over the annular element 1a and the meshes run straight alongthe generatrices of the slightly conical ring 1a is it expedient toeffect the final clamping by means of the screws 44.

A large number of modifications are possible within the scope of theinvention; thus, the function of the rings 33, 34 could be interchangedwith one another by, for example, providing the fastening 27, 28 on theupper ring 34 and the clamping apparatus 29 on the lower ring.

We claim:
 1. Apparatus for covering an annular support of a heart valveprosthesis with an elastic textile covering, said apparatus comprising:two coaxial rings having a central opening for holding the annularsupport together with the covering, a first one of said two coaxialrings having a fastening means for engagement with one end of thetextile covering; and a second one of said two coaxial rings having aclamping device for engagement with the other end of the textilecovering; a stand attached to the first and second rings for holding thefirst and second rings in a predetermined position, said stand includingguide columns slidably attached to said first and second rings forpermitting said first and second rings to be moved along said guidecolumns while maintaining a relative position between said first andsecond rings.
 2. The apparatus according to claim 1, wherein the openingof the first and second rings has dimensions larger than a diameter ofsaid annular support so that a seam can be applied to the textilecovering around the annular support inserted in said opening.
 3. Theapparatus according to claim 1, wherein the clamping device comprises aplurality of clamping elements distributed over a circumference of thesecond ring, each of said clamping elements being provided with agripping element for gripping the textile covering.
 4. The apparatusaccording to claim 3, wherein each of said gripping elements is a hook.5. The apparatus according to claim 1, further comprising an adjustingmeans for adjusting the clamping force applied to the textile covering.6. The apparatus according to claim 5, wherein said adjusting meansincludes a spring.
 7. The apparatus according to claim 1, furthercomprising at least one ring clamping means for holding the first andsecond rings in a position clamping the textile covering.
 8. Theapparatus according to claim 1, further comprising an indicating meansfor indicating the clamping force applied to the textile covering. 9.The apparatus according to claim 1, wherein said stand includes asupporting base that is adjustable in height for holding the first andsecond rings at a desired height.